1. Field of the Invention
The present invention relates to an image pick-up optical system, and more particularly to an image pick-up optical system comprising five lens elements and providing an optical lens assembly with a large field angle, a short total length, and a low cost, and the optical system is applied to an electronic product.
2. Description of the Related Art
As science and technology advance, optical systems for electronic products such as digital still cameras, web cameras or mobile phones tend to be developed with a compact design and a low cost, while meeting user requirements for an optical lens assembly with large field angle, good aberration correction ability, high resolution, and high image quality.
In general, a conventional image pick-up optical system of a compact electronic product comes with different designs, including the two-lens, three-lens, four-lens, and five-or-more lens designs. If the image quality is taken into consideration, the optical lens assemblies with the four-lens and five-lens designs have advantages on aberration correction and modulation transfer function (MTF) performance, and the five-lens design having a higher resolution than the four-lens design is applicable for electronic products of high video quality or high pixel requirement.
In the products such as the mini digital cameras, web cameras, and mobile phone cameras, a compact optical lens assembly with a short focal length and a good aberration is required. In various five-lens designs, an image pickup optical lens assembly with a fixed focal length and different combinations of positive and negative refractive powers are adopted. As disclosed in U.S. Pat. No. 7,710,665, a good aberration correction can be achieved, but the total length of the optical system is still difficult to meet the requirements of a mini electronic device. As disclosed in U.S. patents and publications of U.S. Pat. No. 7,826,151, US2010/0254029 and US2010/0253829, optical systems are designed with a shorter total length by adopting a first lens element with negative refractive power, a second lens element or a third lens element with positive refractive power which is generally called out-phase imaging to obtain a wider field angle. However, the first lens element with the negative refractive power will cause a too-large refractive angle of the light exiting the first lens element and result in an easy light dispersion and a difficult aberration correction of following lenses.
U.S. Pat. No. 7,663,813, U.S. Pat. No. 6,985,309 and U.S. Pat. No. 6,940,662 disclose a first lens element with negative refractive power, and a third lens element and a fourth lens element cemented into a cemented lens to increase the thickness of the lens, so as to reduce the chromatic aberration and the coma aberration produced by the lens assemblies effectively. However, these patents come with in appropriate refractive power of the fifth lens element, and the aberration or distortion of the image is increased. For optical lens assemblies used in mini electronic products, it is necessary to have a more practical design capable of reducing the optical lens assembly, while using the refractive power of the five lens elements, a combination of concave and convex optical surfaces, and the first lens element with positive or negative refractive powers to capture the maximum light of the image, and minimize the air gap between lenses or even form a cemented lens. In addition, the refractive powers of the lenses and the aberration correction ability are adjusted to shorten the total length of the optical lens assembly effectively, so as to improve the image quality, simplifying the manufacture, and apply the optical lens assembly to mini electronic products.